Noble Gas Thermochronometry Lab and (U-Th)/He Chronometry

The Noble Gas Thermochronometry Lab (NGTL) is specifically designed for high-precision and high-accuracy thermochronometry and is currently under construction at BGC. The lab will simultaneously and accurately measure nuclide abundances and temperatures during stepwise thermal extraction of noble gases from minerals and glasses over a wide range of temperatures. Accurate temperature control is essential for noble gas thermochronology.

The design of the NGTL is optimized for 4He/3He thermochronometry and will also be fully operational as both a 40Ar/39Ar thermochronometry and generic NG geochemistry laboratory. 4He/3He thermochronometry requires five quantitative measurements to be made on an individual sample: (a) geometry of the analyzed crystals, (b) temperatures of stepwise heating, (c) 4He/3He ratios during stepwise degassing, (d) total or cumulative stepwise 4He molar abundances, and (e) total U, Th and Sm molar abundances. The lab will be capable of measuring U and Th concentrations for (U-Th)/He dating and the isotopic compositions of all five noble gases will sufficient mass resolution to completely resolve 3He from hydrogen-deuterium (HD) and H3. The later is a capability required for 4He/3He thermochronometry.

The laboratory will consist of:
(i) A calibrated binocular microscope and camera system for preparing and measuring the geometry of samples,
(ii) An automated ultra high vacuum (UHV) noble gas extraction, purification and calibrated standard and spiking system,
(iii) A gas-source quadrupole mass spectrometer (QMS) for measuring NG abundances using isotope dilution,
(iv) An MAP-215 sector-field NG mass spectrometer for high-precision isotope ratio measurements, and
(v) An inductively coupled plasma-source quadrupole mass spectrometer (ICPQMS) for measuring U and Th (and Sm).
The NGTL will be capable of simultaneously performing multiple and automated high-accuracy stepwise degassing analyses and diffusion experiments. Complete system automation and instrument communications will be achieved using software written in LabView.

NGTL Projects
The NGTL was designed to study diverse problems in the Earth and planetary sciences including:
(i) Applications of 4He/3He thermochronometry to study exhumation, erosion rates and timescales of mountainous and high relief topographic development and to test possible influences that climate variability may have on forming relief (e.g., Shuster et al., 2005).
(ii) Applications of 4He/3He and 40Ar/39Ar thermochronometry to constrain the ejection temperatures and long-duration residence temperatures of the Martian meteorites while on Mars (e.g., Shuster and Weiss, 2005).
(iii) Applications of (U-Th)/He and 4He/3He chronometry to study timescales and rates of chemical weathering at Earth’s surface (e.g., Shuster et al., 2004 and Heim et al, 2006)
(iv) Applications of cosmogenic nuclides (e.g., 3He, 21Ne, 38Ar) to constrain long-term exposure timescales of samples near Earth’s surface
(v) NG diffusion kinetics in a range of natural materials to advance our basic understanding of solid-state diffusion and potentially identify novel applications of the noble gases.

If you are interested in collaborative use of the lab or have an interesting problem in need of high-precision thermochronometry, please contact David Shuster.